EP2696988A1

EP2696988A1 - Device and method for conveying powder from a powder supply

Info

Publication number: EP2696988A1
Application number: EP12709597.4A
Authority: EP
Inventors: Stefan Nettesheim
Original assignee: Reinhausen Plasma GmbH
Current assignee: Maschinenfabrik Reinhausen GmbH
Priority date: 2011-04-15
Filing date: 2012-03-13
Publication date: 2014-02-19
Anticipated expiration: 2032-03-13
Also published as: US20140105694A1; US9327919B2; CN103476511B; WO2012139840A1; JP6181041B2; EP2696988B1; JP2014516892A; CN103476511A

Abstract

A device and a method for conveying powder (1) are disclosed. A container (2) is provided for the powder (1), wherein the powder (1) defines a surface (18) in the container (2). A suction means (6) has a suction opening (7) for sucking in the powder (1) from the surface (18). A moving means (44) serves for producing a relative movement (8) between the suction opening (7) and the surface (18) of the powder (1). During the relative movement (8), the powder (1) is sucked in, a speed (V) of the relative movement (8) being variable in such a way that there is a constant mass flow (M).

Description

DEVICE AND METHOD FOR PROMOTING POWDERS

A POWDER ADVICE

The invention relates to a device for conveying powder. In particular, the device comprises a container for the powder, wherein the powder in the container defines a surface. A suction means, which is provided with a suction opening, serves for sucking the powder from the surface.

Furthermore, the invention relates to a method for conveying powder from a container for the powder. Such devices and methods are used, for example, for supplying metered quantities of fine-grained powders for plasma coating processes. Powder deposits and agglomerations of the powder must be avoided, since otherwise the delivery of the powder can come to a standstill. The promotion of fine powder with particle sizes of less than 150 μιη is possible with known conveyors only with considerable restriction of the accuracy of the delivered mass flow. For particles below 20μιη and flow rates of less than 10 g / min, there is no technically ideal solution. Below this grain size, the adhesion forces between the powder particles increase considerably. The surface of the particles increases considerably in relation to the volume. A cube with an edge length of 1 cm has a surface of 0.006 m ² . The same volume filled with particles of five nanometers edge length, however, has a surface area of 2,400 m ² . The large increase in surface forces hinders the promotion of such small particles. By permanent energy coupling, in particular high flow velocities, which are associated with a high gas or air consumption, agglomeration of the powder / gas mixture can be avoided. High gas flow rates, however, are in different

downstream work processes, such as plasma Coating processes or laser coating processes, disadvantageous. In addition, high gas flow rates require a higher energy input for the promotion. Furthermore, small amounts of fine-grained powders can not be dispersed with gas.

DE 44 23 197 discloses a powder pump for powder for spray coating of articles in a rod-like elongated shape. On one end, the powder pump has a powder suction, is sucked through the powder from an open-topped powder container and conveyed through an inner tube of the powder pump to a consumer. The promotion itself is done by generating a vacuum in the powder pump. The vacuum is created with an injector nozzle located near the powder suction port.

DE 10 2006 002 582 A1 discloses a powder conveyor with a fluidising unit. The fluidizing unit is arranged at the end of a powder suction pipe of the powder conveyor and blows in the intake of the Pulveransaugrohrs fluidizing air in the powder supply, so that the powder can be fluidized and thus easier to be sucked and transported. The fluidising unit is arranged above and concentric with the powder suction opening. As a result, a screen-shaped fluidized powder region forms around the intake opening. The promotion is carried out by means of an injector operating with compressed air, which on the fluidizing unit

opposite end of the Pulveransaugrohres is connected. A

Fluidization directly below the Pulveransaugöffnung done by design not. Although the annular fluidization improves the suction of the powder, the constancy of the amount of powder in the suction is not optimal. Furthermore, agglomerates of the powder are insufficiently dissolved and largely sucked directly through the powder suction. This leads in particular

Downstream coating processes that require a consistent layer thickness, problems.

Based on this prior art, the invention is based on the object to provide a device for conveying powders, so that the amount of the delivered powder is constant over time. This object is achieved by a device having the features of claim 1. Another object of the invention is to provide a method for conveying powders such that the amount of powder delivered over time

predetermined value corresponds.

According to the invention, the suction of the powder takes place exclusively by a

Surface of the powder contained in the container. The suction can also take place from or from a surface of the powder containing the powder surface. In particular, in the case of a powder supply of fine-grained, non-flowable powders, cavities, which are only to be removed by intensive action on the surrounding powder supply, are formed on being aspirated from the lower powder layer. The cavities are characterized by an uneven flow rate (mass flow) in the promotion of the powder noticeable. Moving means generate one

Relative movement between the suction port of the aspirator and the surface of the powder or the cover layer during the suction of the powder. As a result, the required mechanical energy is coupled into the powder in order to prevent the formation of cavities in the cover layer. A movement means is used to generate a relative movement between the suction port and the

Surface of the powder during the suction of the powder. A speed of the relative movement is variable such that a predetermined mass flow from a first working space to a second working space prevails, so as to transport the powder in the container to the substrate.

The manner of aspirating the powder depends on the mass and size of the individual powder particles. According to one embodiment, the suction means may be spaced from the surface of the powder. Furthermore, it is possible that the

Aspirator touches the surface of the powder. Likewise, as already described above, the aspirator dips into the top layer of the powder. The

Suction in the cover layer preferably takes place as close as possible to the surface of the powder at a distance from the suction opening of the suction means to the surface eles powder supply in a range of 1 to 10 mm. This near-surface

In the case of fine-grained powders with particle sizes of 0.01 to 100 μm, suction always ensures that the trace produced by the suction agent in the covering layer is or remains open to the surface of the powder.

As already mentioned, it is conceivable that the suction means (powder trunks or suction needle) is guided without any distance to the surface of the powder. With very light powder, the suction can be performed without direct contact with the powder surface. This means that the suction means in this case is spaced approximately 0, 2 mm from the powder surface and is guided at this distance to the powder surface. There is thus no direct mechanical contact between the aspirator and the powder surface. Due to the suction flow, the powder is torn from the powder surface and transferred into the suction means. The volume flow of the pumped powder can be changed if the

Speed of relative movement between the suction port and the

Powder supply is adjustable. Furthermore, the geometry of the suction means and the diameter of the suction opening has a significant influence on the

Volume flow of the pumped powder. Of the aforementioned parameters, the preferred distance of the suction port of the aspirator to the surface of the powder supply depends. Larger volume flows allow a greater distance of the suction opening and thus the suction and removal of a thicker powder layer during the relative movement of the suction in the cover layer. In particular, three-axis systems which permit a movement of the suction means in the X, Y and Z directions come into consideration as movement means for generating the relative movement. The X / Y movement is for generating the horizontal

Relative movement between the suction port and the surface of the powder or powder within the cover layer required while the Z-axis of the vertical tracking of the suction port is at a constant distance to the surface of the powder, a constant contact of the surface of the powder or a constant immersion depth of the suction to ensure in the top layer. The Tracking the suction is required when a whole layer of the powder has been removed with the suction.

The suction means preferably has a needle-shaped, hollow cylindrical body with two end faces, wherein one of the end faces forms the suction opening, while the other end face is preferably connected via a flexible suction line to the suction side of a pump whose pressure side the powder downstream process, in particular a plasma Coating process, feeds. One possibility for automated tracking of the suction opening in the direction of the Z axis of the powder supply is that a buoyant body is arranged on the suction means at a distance from the suction opening. The buoyant body is such that it floats on the surface of the powder supply and thus adapts to the surface of the powder supply. The float ensures a constant distance of the suction opening to the powder surface within the cover layer.

The adjustment of a pressure difference between the first working space and the second working space serves to convey the powder from the surface of the powder in the container to a surface of a substrate. One way to adjust the pressure difference is a diaphragm pump.

The powder to be delivered is separated in such a pump through the membrane of the drive. By this separation membrane, the drive is protected from the harmful effects of particular fine-grained powder. Furthermore, the fine-grained powder is separated from any influences by the drive, in particular lubricants. The deflection of the membrane is preferably carried out pneumatically or mechanically. The oscillation frequency of the membrane for conveying fine powders is preferably in a frequency range of 10 Hz to 200 Hz with a pump volume in a range of 0.1 to 20 ml.

If the aspirator is connected to at least two diaphragm pumps which can be operated in phase displacement, unwanted pulsation of the powder in the diaphragm can occur Pressure line avoided, or at least reduced. The high frequencies of the membrane pump promote the continuous promotion of small quantities of fine-grained powder. For the continuous, low-pulsation promotion fine powder, it is advantageous if each diaphragm pump is connected at its suction side via a shortest possible suction line with the suction means. A length of the suction line of 1 to 50 cm has proven advantageous, while the length of the pressure line for pulsation-poor delivery is preferably at least 10 times longer. In experiments with suction and discharge lines with an inside diameter of 2.5 mm, no low-pulsation conveyance with pressure line lengths of 3 m could be achieved, while good results were achieved with pressure line lengths of more than 10 m. The length of the suction line was in the experiments 0.5 to 1 m.

From the experiments, it was recognized that a uniform, low pulsation promotion of the fine powder is achieved when each diaphragm pump is connected to a pressure line at the pressure side and the length of the pressure line exceeds its diameter by at least a factor of 2000.

In order to avoid powder deposits in the conveying path, the suction means and / or the suction lines and / or the pressure lines of the device are preferably connected to a vibration exciter. If the aspirator is connected to a vibration exciter, the powder is loosened in the vicinity of the surface or in the cover layer in the region of the intake and

Powder agglomerates are destroyed before aspiration and in the aspirator itself. By a superimposed oscillating movement, such as in the form of a circular oscillation of the suction, several positive effects are achieved with respect to the sucked and conveyed powder amount. The powder surface is smoothed and so a constant or predetermined flow rate of powder can be maintained. The area swept by the aspirator per unit time is increased, averaging a possible discontinuity in the nature of the powder surface. Both effects ensure a constant compliance with a certain delivery rate (a given mass flow). For example, mechanical vibrators or piezoelectric vibrators are used as vibration exciters.

The promotion of fine-grained powders can be improved by fluidizing the aspirated powder in the suction means and / or downstream of the suction means while supplying a gas. The fluidizing gas is admixed in particular at a low volume flow of 1 l / min to 50 l / min.

For the purpose of fluidization, the suction means may be designed as a hollow needle. An inner hollow needle serves as a suction means, while the fluidizing gas is supplied via an outer hollow needle surrounding the inner needle.

So that a predetermined mass flow of the powder from the container to the substrate can be ensured, the container stands on a balance. The balance is connected to a measuring and control electronics which controls the movement means or the multi-axis system in such a way that the predetermined mass flow of the powder is adjusted or maintained from the surface of the powder to the surface of the substrate via the speed of the relative movement. The horizontal relative movement in the top layer can be done with the help of

Movement means are circular. To even out the level of the powder surface, it is also possible to provide a device for leveling the powder surface, for example a rake moving relative to the powder surface, which presses the powder from the adjacent regions into the track in the cover layer caused by the suction means after suction of the powder. As a result, after a circular relative movement of 360 ° only a small tracking of the suction in the direction of the Z-axis is required.

Is the horizontal relative movement in the cover layer with the help of

Running means spiral, this relative movement allows the complete removal of a powder layer over the entire surface of the

Powder supply without mechanical action on the areas adjacent to the track produced by the suction means. The method of conveying powder comprises the following steps:

Aspirating a powder through a suction port of a suction means from a surface of the powder in a container; · Generating a relative movement between the suction port and the

Surface of the powder during the aspiration of the powder;

• continuously weighing the weight of the powder in the container during the aspiration of the powder, the measurement data being transferred to a measuring and control electronics; and

· Setting a speed of relative movement between the

Intake port and the surface of the powder that a predetermined mass flow of the powder is obtained from the container.

The invention will be explained in more detail with reference to the figures. Show it:

FIG. 1 shows a schematic side view of a device according to the invention for conveying fine-grained powder,

FIG. 2 shows the apparatus according to FIG. 1 for conveying fine-grained powder to a plasma coating installation,

FIG. 3 a shows a representation of a spiral relative movement with respect to the surface of the powder supply,

FIG. 3b shows a representation of a meander-shaped relative movement with respect to the surface of the powder supply,

3c shows a representation of a rectilinear relative movement with respect to the surface of the powder supply, FIG. 4a shows a schematic side view of a further embodiment of a device according to the invention with a circular relative movement with respect to the surface of the powder supply, Figure 4b is a plan view of the device of Figure 4a and

Figure 5 is a schematic representation of a control for setting a time predetermined mass flow of the subsidized with the suction powder.

Figure 1 shows an apparatus for conveying fine-grained, non-flowable powder 1 with particle sizes of 0.01 μιη to 100 μιη. The powder 1 is stored in a container 2. The powder supply has a cover layer 3, not shown to scale in the figure, with a constant thickness 4 of 20 mm. Below the cover layer 3 or a surface 18 of the powder 1 is a lower layer 5 of the powder supply, whose thickness at the beginning of the suction of the powder 1 from the

Powder supply is many times greater than the thickness 4 of the cover layer 3rd

The device further comprises a suction means 6 with a suction opening 7 for sucking the powder 1 from the container 2. The suction means 6 is designed in the illustrated embodiment as a hollow needle. The hollow needle is on a multi-axis system 41 as a means of movement for generating a

Relative movement 8 in the X direction X and Y direction Y between the suction port 7 and the powder 1 within the cover layer 3 is arranged. Likewise, it is conceivable that the suction opening 7 of the suction means 6 to the surface 18 of the powder 1 is guided at a distance of 0mm or slightly spaced from the surface 18 of the powder 1. A distance from the surface 18 of the powder 1 may prevail if the particles of the powder 1 are light enough to move from a first working space 51, in which the surface 18 of the powder 1 is located, to a second working space 52, in which a Surface 35 of a substrate 36 (see Fig. 2) is to be transported. Between the surface 18 of the powder 1 and the surface 35 of the substrate 36, a pressure difference Δρ prevails. In this case, the particles of the powder 1 are sucked out of the surface 18. At the end of the suction means 6 opposite the suction opening 7 there is a gas feed 9 for supplying fluidizing gas 10 into the mass flow

In addition, the suction means 6 is a mechanical one

Vibration generator 1 1 arranged, the agglomerations of the powder 1 in the Dissolves passage of the suction means 6 and the powder 1 loosens in the surface 18 and in the cover layer 3 in the region of the suction port 7.

One possibility for adjusting the pressure difference Δρ between the surface 18 of the powder 1 and the surface 35 of the substrate 36 or between the first

Working chamber 51 and the second working chamber 52 is a diaphragm pump 12. In this case, the diaphragm pump 12 is on a suction side 13 via a

Suction line 14 is connected to the suction means 6. At the pressure side 15 of the

Diaphragm pump 12 is connected to a pressure line 16 which leads to a plasma coating device 17 not shown in detail in Figure 1, whose function and operation will be explained below with reference to Figure 2.

With the help of the multi-axis system 41, not shown in Figure 1 is a

Relative movement between the suction port 7 and the powder supply within the cover layer 3 and with respect to the surface during the suction of the powder 1 by means of the diaphragm pump 12 is generated. The immersion depth of the suction opening 7 is during the entire horizontal movement through the cover layer 3 in a range between 1 to 10 mm. The device shown in Figure 1 may comprise a plurality of suction means 6, the one or more multi-axis systems 41 simultaneously relative to the

Powder supply within the cover layer 3 or in relation to the surface to be moved. The multi-axis system 41 for generating the relative movement 8 can be embodied, for example, as a gantry system or as a robotic arm of a robot.

The multi-axis system 41 can perform the relative movements 8 between the aspirator 6 and the surface 18 of the powder 1 shown by way of example in FIGS. 3 a to 3 c. In order to suck off a powder layer P (see FIG. 1) over the entire surface 18 of the powder 1, a horizontal relative movement 8 of rectilinear components in the x-direction X and y-direction Y is composed. As can be seen from the plan views of Figure 3a to Figure 3c. After the powder layer P has been removed, the surface F exposed by the powder removal forms the new surface 18 of the powder supply. The suction port 7 is with Help the multi-axis system 41 tracked in the z-direction to position the suction port 7 in the upwardly limited by the new surface 18 new cover layer 3 (see Figure 1). Subsequently, the fine-grained powder 1 is sucked off near the surface from the new covering layer 3 with the suction means 6. The

Spacing possibilities or the immersion depth of the suction means 6 in the powder 1 is described in detail above. Although FIGS. 1 and 2 illustrate immersion of the aspirator 6 into the powder 1, this should not be construed as limiting the invention. Figure 3a shows a horizontal spiral relative movement 8 within the

Cover layer 3 or with respect to the surface 18 of the powder 1, which can also be generated by means of a suitable control with the multi-axis system 41. FIG. 3b shows a horizontal meander-shaped relative movement 8 within

Covering layer 3 or with respect to the surface 18 of the powder 1. Figure 3c shows a horizontal rectilinear relative movement 8 within cover layer 3 or with respect to the surface 18 of the powder 1, which is composed of a plurality of rectilinear trajectories 50. The tracking takes place with all possible trajectories 50, in z direction Z. FIGS. 4 a and 4 b show a further embodiment of a device according to the invention which has a circular relative movement 8 (consists of components in the x-direction X and the y-direction Y together) between the suction means 6 and the surface 18 of the powder 1 in the container 2. Components of the device according to FIG. 4 which correspond to the exemplary embodiment according to FIG. 1 are provided with matching reference symbols. In that regard, reference is also made to the statements there.

In the embodiment shown here, the device comprises a rotary drive 20 with which the container 2, which is circular cylindrical in cross-section, surrounds its container

Rotation axis 21 can be set in rotation. In general, however, the rotary drive 20 is omitted. On a horizontal cantilever 24 of the frame 22 in the z-direction Z is

height-adjustable suction 6 arranged. The suction opening 7 pointing in the direction of the surface 18 of the powder 1 can protrude into the cover layer 3 or, as shown in FIG. 4 a, only touches the surface 18 of the powder 1.

Of course, it is also possible in the context of an embodiment of Figure 4, the suction means 6 itself with a drive for tracking the

To provide suction means 6 in the z-direction Z. Figure 2 illustrates an application example of the device according to the invention. The pressure side 15 of the diaphragm pump 12 is through the pressure line 16 with a beam generator 31 for generating a collimated plasma beam 32 through

Arc discharge connected. In the plasma jet 32 of the jet generator 31, the powder / gas mixture in the region of the outlet 34 in a

Feeding area introduced by means of a nozzle 33. The finely divided powder 1 is deposited with the plasma jet 32 on the surface 35 of a substrate 36 as a coating 37. To generate the plasma jet 32, the jet generator 31 has an inner, rod-shaped electrode 38 and a jacket electrode 39 which is surrounded and insulated against the inner rod-shaped electrode 38, through which a working gas 40 flows through from the opening 33 opposite the nozzle 33.

The distance between the suction opening 7 to the surface 18 of the powder 1 can by the effective also in the z-direction multi-axis system 41 within the

Cover layer 3 or in relation to the surface 18 of the powder 1 can be specified.

FIG. 5 shows a schematic arrangement 23 with which a predetermined mass flow

^ of the conveyed by the suction means 6 powder 1 is made possible. The container

2 stands together with the powder 1 on a balance 42. By constant weighing of the mass M of the powder 1 in the container 2 during the suction of the powder 1, one can determine the per unit time extracted amount of the powder 1. The won are transferred to a measuring and control electronics 43. Between the balance 42 and the measurement and control electronics 43, an operational amplifier 26 is provided. The balance 42 is connected to the measurement and control electronics 43, which Achssystem 41 controls such that the velocity V of the relative movement 8 of the predetermined mass flow of the powder 1 from the surface 18 of the powder 1 to the surface 35 of the substrate 36 can be maintained. The measuring and

Control electronics 43 receives the actual value I of the mass flow ^ (first derivative of the transported mass M after the time t) as a function of time. The

Change in mass flow is the second derivative of the transported mass after time. The measurement and control electronics 43 performs a comparison between the actual value I and the setpoint value S. The diaphragm pump 12 also provides information about its status to the measurement and control electronics 43. On the basis of the comparison, a controlled variable V _s for the velocity V of the relative movement 8 is generated.

The determined controlled variable V _s is used to control and regulate the means for generating the relative movement 8 between the suction means or the

Intake port 7 and the surface 18 of the powder 1, wherein the suction is not interrupted. Due to the controlled variable V _s , the velocity V is the

Relative movement 8 changed so that a timed mass flow prevails ^.

LIST OF REFERENCE NUMBERS

No. Designation

1 powder

2 containers

3 topcoat

4 thickness

5 lower layer

6 aspirating agent

7 suction opening

8 relative movement

9 gas supply

10 fluid isierungsgas

1 1 vibration exciter

12 diaphragm pump

13 suction side

14 suction line

15 print side

16 pressure line

17 plasma coating device

18 surface

19 surface

10 pressure drive

21 rotation axis

22 frame

23 arrangement

24 cantilever

26 operational amplifiers

27 segment

28 rope

29 pulleys

30 counterweight

31 beam generator

32 plasma jet

33 nozzle

34 outlet

35 surface

36 substrate

37 coating

38 rod-shaped electrode

39 sheath electrode

40 working gas

41 multi-axis system

42 Libra

43 Measuring and control electronics

44 means of movement

50 trajectory

51 first working space

Claims

claims:

Device for conveying powder (1) comprising:

A container (2) for the powder (1), wherein the powder (1) in the container (2) defines a surface (18), and

A suction means (6) having a suction opening (7) for sucking the powder (1) from the surface (18), characterized in that

• a movement means (44) for generating a relative movement (8) between the suction opening (7) and the surface (18) of the powder (1) during the suction of the powder (1) is provided, wherein a speed (V) of the relative movement (8 ) is variable so that a given mass flow (^) prevails.

Apparatus according to claim 1, wherein the suction means (6) is spaced from the surface (18) of the powder (1).

Apparatus according to claim 1, wherein the suction means (6) contacts the surface (18) of the powder (1).

Apparatus according to claim 3, wherein the suction means (6) dips into a cover layer (3) of the powder (1).

Device according to one of claims 1 to 4, wherein the movement means (44) comprises a multi-axis system (41) for generating the relative movement between the suction port (7) and the surface (18) of the powder (1).

Device according to one of claims 1 to 6, wherein the suction means (6) comprises a hollow cylindrical body with two end faces, wherein one of the end faces forms the suction opening (7).

7. Device according to one of claims 1 to 6, wherein a pressure difference (Δρ) between the surface (18) of the powder (1) in a first working space (51). and a surface (35) of a substrate (36) in a second working space (52) prevails, wherein the powder (1) to the working space (52) is conveyed.

8. Device according to one of claim 7, wherein the pressure difference (Δρ) with at least one diaphragm pump (12) can be generated.

9. Device according to one of claims 1 to 8, wherein the suction means (6) and / or the suction line (7) and / or the pressure line (16) with a vibration exciter (1 1) are connected.

10. Device according to one of claims 1 to 9, wherein the suction means (6) comprises a supply for a fluidizing gas (10).

1 1. Device according to one of claims 1 to 10, wherein the container (1) on a balance (42) is, and the balance (42) with a measuring and

Control electronics (43) is connected, which controls a multi-axis system (41) such that on the speed (V) of the relative movement (8) of the predetermined mass flow (^) of the powder (1) from the surface (18) of the

Powder (1) to the surface (35) of the substrate (36) is maintained.

12. A method of conveying powder (1) comprising the steps of:

• sucking a powder (1) through a suction port (7) of a

Suction means (6) from a surface (18) of the powder (1) contained in a container (2);

Generating a relative movement between the suction port (7) and the surface (18) of the powder (1) during the suction of the powder (1);

• continuously weighing the weight of the powder (1) in the container (2) during the suction of the powder (1), wherein the measurement data are transferred to a measurement and control electronics (43); and

• Setting a speed (V) of the relative movement (8) between the suction port (7) and the surface (18) of the powder (1), that a predetermined mass flow (^) of the powder (1) from the container (2) is achieved ,

13. The method of claim 12, wherein with a balance (42) a time change of the mass (M _T ) of the powder (1) in the container (2) is determined and the measuring and control electronics (43) the speed (V) in such a way Changes to set the default mass flow (^).

14. The method according to claims 12 to 14, wherein a pressure difference (Δρ) between the surface (18) of the powder (1) in a first working space (51) and a surface (35) of a substrate (36) in a second working space ( 52) by means of which the powder (1) is conveyed to the substrate (36).

15. The method of claim 14, wherein, the pressure difference (Δρ) with at least one diaphragm pump (12) is generated.

16. The method according to any one of claims 12-15, wherein the sucked powder (1) in the suction means (6) and / or the suction means (6) downstream lines is fluidized with the supply of a gas.